A commonplace type of WLAN system is the 802.11 IEEE (Institute of Electrical and Electronics Engineers) standard. Up until 2004, 802.11 wireless devices had a single antenna (some devices had two antennas, but there was only one set of components to process the signal, or RF chain). 802.11 task group N (TGn) has recently proposed an 802.11n standard that has the goal of increasing the peak data throughput transmitted by a wireless multiple-input/multiple-output (MIMO) device to 100 Mbps. The basis of MIMO operation is to provide 11n devices with multiple radio interfaces to allow the devices to send data on different channels at the same time in order to achieve greater transmit/receive data rates than the pre-11n devices.
In a WLAN, information is transmitted between a transmitter and a receiver through the transmission of encoded data packets. These data packets are then decoded at the receiver based on channel state information (CSI). The more accurate the CSI, the more accurate will be the decoding precision, and hence lower the packet error rate. Because a WLAN may suffer from impairments such as delay spread, thermal noise, and bandwidth fluctuations due to a shared medium with multiple users in a mobile environment, a perfect CSI is never known to the receiver. Instead, the receiver must rely on channel estimation. In a WLAN, such as 802.11n, channel estimation is performed at the receiver through training sequences that are transmitted prior to the data. The training sequences are pre-determined and known to the receiver, enabling the receiver to estimate the CSI. For example, in a WLAN 802.11n system, the packet structure includes a preamble that is followed by the data. The preamble includes several types of fields, including several training fields.
Although the other types of fields in the preamble include a variety of information, currently, channel estimation performed at the receiver is restricted to use of only the training fields of the packet preamble. Accordingly, by limiting the channel estimation to only use of the training fields of the preamble, the accuracy of the channel estimation may be likewise limited.